The conventional computer keyboard is based on the keyboard of a standard English typewriter with several additional edit keys and function keys. Among these keyboards, the number of keys on each keyboard varies from tens to over a hundred, e.g., the keyboard of an Apple Computer has 52 keys, IBM-PC has 83 keys, and PS-2 has 101 keys, etc., and the keyboard of some computers may have even more keys. The reduction in size of the keyboard will become very difficult if it has too many keys. Or even if it was reduced, owing to the fact that the keys are located too closely, the typing operation would be hindered by frequent mistouch, this would affect the effectiveness of using the keyboard. The currently used methods of inputting characters on a conventional computer keyboard are mainly direct methods. That is, with the characters assigned to the keys respectively in one to one correspondence. Though these methods are straight forward, they have some significant drawbacks: first, with the expansion of input character set, the number of keys will also increase; and second, the marks tagged on the keys will have to be changed when the input character sets are changed. This not only brings about difficulty to the miniaturization of the keyboard but also causes inconvenience in inputting of large character sets or alteration of input character sets.
The invention entitled "An Zi Jie Multi-functional Language Processing Device on coding basis--An Zi Jie Writing Machine", as disclosed in the Chinese Patent No.: 861048501 is intended to solve this problem. It suggests a small keyboard with 20 keys. On the top of each key two letters, one numeral or punctuation mark and other pattern or script are tagged. Though the number of keys on this keyboard has been reduced, it can only input characters that are tagged on the keys in a direct way. For those characters that are not tagged on the keys, it is necessary to adopt a coding method to input them, but to memorize a large number of codes is hard work. If characters of different languages are involved, it is necessary to alter the marks tagged on the keys. This would cause even more inconvenience when characters of several different languages are to be inputted.
To input Chinese characters is a hard problem. It is even more difficult to input Chinese characters on a standard English keyboard. If inputted by phonetic codes, duplication code rate will be very high and it is impossible to type without looking at the keyboard. In order to input the Chinese characters by structural coding method, over six hundred Chinese character parts are to be distributed to and tagged on the keys respectively. Owing to the large number of the parts involved, the keyboard can not hold them. But we may select out of them about 100 or so frequently used parts and tag them to the letter and numeric keys thus the input of Chinese characters can still be carried out by structural coding method on a conventional keyboard. The invention entitled "Optimized Five-stroke Coding Method and Its Keyboard", as disclosed in Chinese Patent for invention No.: 85100837 works in the following way. Since one letter is used to represent several parts, duplication codes are unavoidable when a number of different parts are being used to code a character. In order to reduce duplication codes, it is necessary to adjust the combination of parts on each key and this will surely lead to a situation where the parts tagged on a single key are quite different to each other in shape. This makes it difficult to remember the locations of more than one hundred parts on the keyboard. Five-stroke coding method lists more than one hundred and ninety frequently used parts. It is necessary to remember mechanically all parts represented by the letters. The problem of duplication code still exists and it is necessary to distinguish the duplication codes by combining "pattern" and "last stroke" to form an identification code. It is very inconvenient to operate.
It is likewise inconvenient to input the graphical symbol by a standard English keyboard, on which there are no proper elementary patterns suitable for constructing graphical symbols tagged. In order to input a designated graphical symbol (for example, the symbol of a transistor), it is necessary to use a letter or a numeral to stand f or it. If we tag the graphical symbol to be inputted on the keys, then it would be troublesome to change to a different set of graphical symbols. If the correspondence relationship between graphical symbol and its designated numeral is displayed on the screen, the screen space available for the user would be smaller.